Catheter

ABSTRACT

The invention relates to a catheter arrangement which comprises at least a first basic element and a second basic element, which second basic element is arranged such that it is slidably arranged in the first basic element over at least part of its length and has a sensor unit that is provided for determining a position and/or mutual position shift of the first basic element and the second basic element, to generate at least a sensor value that is assigned to a measurable property of the catheter arrangement. The repeated reaching of a once-defined position is allowed by such a catheter arrangement, so that after expanding a vessel constriction, a stent can be taken to the same position without having to take X-rays for verification of the position, which are burdensome to the patient.

The invention relates to a catheter arrangement comprising at least twobasic elements.

Catheters, which are used in medical technology for diagnostic orsurgical processes, have at least two basic elements: a catheter sleeveand an instrument catheter, which is moved within the catheter sleeveafter placing it in the catheter sleeve, so that the instrument whichthe instrument catheter typically has on its tip is pushed into thedesired place inside the patient and is then located is outside thecatheter sleeve. A catheter, as is used, for example, in intercoronaryarterial operation, mainly comprises three basic elements, namely acatheter sleeve, which has a relatively large diameter (about 2-3 mm), aguide wire with a relatively small diameter (about 0.25 mm) and aninternal catheter, which can be moved inside the catheter sleeve overthe guide wire. Catheter arrangements with two or three basic elementsare also known in other applications, such as for minimum invasiveinterventions or in endoscopic examinations. The size ratios differ fromthose for intercoronary arterial applications, according to theapplication.

In an intercoronary arterial operation, the catheter sleeve isintroduced in an artery in the groin or the shoulder of the patient andis pushed up to the heart as far as the ostium. The catheter sleevecannot be pushed any further in this application due to its largediameter. The guide wire, typically with an elastic head, is movedfurther into the coronary arteries, till the guide wire tip has beenmoved ahead behind the arterial region to be treated (for example anarterial constriction). The positioning is done with the help of X-rayfluoroscopy sequences with a contrast medium, to make the coronaryartery free and the anomaly to be treated (for example a constriction)appear in the fluoroscopy images., Besides the contrast medium injectionalso X-rays for positioning are made. Both are burdensome to thepatient.

First an internal catheter is moved over the guide wire. It typicallybears an instrument on its tip, about an inflatable balloon, by means ofwhich the coronary artery constriction can be expanded. In a secondstep, the internal catheter is pulled out again and a second internalcatheter is introduced, which has what is called a stent, which is athin wire mesh, used for stabilizing the expanded portion of thearterial area. The stent must then come to be at the same location, atwhich also the artery was expanded. This is again done typically withthe help of fluoroscopy recorded images. These are an additional burdento the patient and it would be desirable to reduce this burden.

It is therefore an object of the invention to improve the cathetermanagement, so that the burden to the patient is reduced.

The object is achieved through a catheter arrangement, which comprisesat least a first basic element and a second basic element, which ismovably arranged over at least a part of its length within the firstbasic element, and which catheter arrangement has a sensor unit providedfor generating at least a sensor value which is assigned to a measurableproperty of the catheter arrangement, for determining a position and/ora position shift of the first basic element and the second basic elementto each other.

The advantage of the invention as claimed in claim 1 is that it renderspossible the determination of the position or the mutual position shiftof two basic elements, say, the position of the inner catheter relativeto the guide wire or to the catheter sleeve. A position reached once canthus be easily reached again without needing the burdensome X-rays. Thistakes place by comparing two position shifts or positions. If the firstinstrument (for example the balloon) has been placed, then either theshift is measured or the position at the location of use of theinstrument is measured when the instrument catheter is pulled out. If asecond instrument catheter, with its instrument (for example the stent)is pushed in again, the same position shift can be made in anotherdirection or the shifting is done till the same position is measuredagain. The sensor unit used for measuring then measures a measurableproperty. The measurable property can be regular markings, which can bemeasured electromagnetically, mechanically or optically, magneticallyrecorded information or only the property of the guide wire, having acertain resistance in a power circuit from one end up to the position ofthe sensor, which resistance can be assigned to a position. Dependingupon the type of the measurable property, it allows to determine aposition by means of a sensor value or to determine a position shift bymeans of two or more sensor values (this includes a continuous readingof the sensor values).

Claim 2 shows a particularly advantageous embodiment. Using a sensor,which is located on one of the basic elements, a measurable propertyshown by another basic element can be measured and the sensor values canbe converted into a position value or a position shift value.

A special embodiment of the measurable property is a structuring. Astructuring can be a mechanical, electromagnetic or optical property.

Another advantageous embodiment of the invention is provided if thestructure of the structured basic elements can be measured withouttouching them, because contact always entails wear and tear andmechanical resistance, which can be avoided by contactless measuring.

Another advantageous embodiment of the invention is provided if thestructuring of the structured basic elements varies in the longitudinaldirection, as described in claim 5. This, for example, indicates havinga uniform structure, which allows a position shift determination bysimple counting off of the measured rings.

The invention can have a particularly advantageous embodiment if thereare two sensors, which measure the regular structuring. Because if thedistance between the two sensors is smaller than the width of thestructuring; the direction of movement can be determined and multiplepulling forward or backward in the positioning operation can be takeninto account.

If the regular structurings are structurings of the electromagneticproperties, as described in claim 6, then it is mostly easy to realizethe sensor, for example, as a simple contact or as a capacitancemeasuring sensor. If the electromagnetic property is the connectivity,the structuring can also be realized easily, say, by simple insulation.

In another advantageous embodiment of the invention the sensor unit hasa sensor evaluation unit, which can convert the sensor values of thefirst sensor into position values or into position shift values.

A typical embodiment of the catheter arrangement has a basic elementthat is elongated and hollow, so that it is easy to achieve a shiftcapability for a second basic element in the first basic element.

The invention further relates to a method for determining the positionand/or a position shift of a first basic element and a second basicelement of a catheter arrangement, in which method the second basicelement is arranged so that it can be moved over at least a portion ofits length in the first basic element, in which a sensor unit generatesat least a sensor value which is assigned to a measurable property ofthe catheter arrangement.

These and the other aspects of the invention are apparent from and willbe elucidated with reference to the embodiments described hereinafter.In the drawings,

FIG. 1 schematically shows a catheter arrangement comprising the threebasic elements that can be moved into each other.

FIG. 2 schematically shows a structuring of the guide wire, where theguide wire is also linked to a supply unit,

FIG. 3 shows the inner catheter, which can be shifted in longitudinaldirection relative to the guide wire and has two sensors in contact withthe guide wire which are connected to a sensor evaluation unit, and

FIG. 4 shows an inner catheter and a structured guide wire, where theinner catheter has two sensors which measure the structuring of theguide wire without contact,

FIG. 5 shows a side detail of a structured guide wire, that has threestructural elements and two ring electrodes that are arranged on theinner catheter, which is not drawn, and

FIG. 6 shows a cross-section through the structured guide wire and aring electrode with three contact points.

A catheter arrangement comprising the basic elements, catheter sleeve,inner catheter and guide wire, is used for intercoronary arterialapplications in the blood—filled arteries of a patient. It will bedepicted below, how such a catheter arrangement can be arranged to makeit possible to determine a position value or a position shift value,resulting in less burden on the patient, if a position has to be reachedmore than once. The catheter arrangement need not, however, berestricted to three basic elements, because the invented embodiment alsofunctions with two or more than three basic elements.

FIG. 1 schematically shows the three basic elements of a catheterarrangement for intercoronary arterial applications. The catheter sleeve1 is the outermost of the three basic elements. Within the cathetersleeve there is the inner catheter 2 which can be moved over a guidewire 3 (also called guide wire). The guide wire 3 is the innermost ofthe three basic elements. The three basic elements often have differentlengths (e.g. the guide wire 3 is typically designed longer than thecatheter sleeve 1). The three basic elements are arranged to be capableof moving essentially independently of each other.

FIG. 2 schematically shows a structuring of the guide wire 3.Structurings 3′ are provided on the guide wire 3 or incorporated withit. Another embodiment is the measurable property of the Ohmicresistance between a fixed contact point and the point defined by ashiftable contact. In the embodiment shown the guide wire 3 is connectedto a supply unit 4, which makes it possible to maintain the guide wire 3continuously at a voltage potential or to supply it with energy (e.g. inthe form of current) or light.

FIG. 3 shows the structured guide wire 3 with the inner catheter 2 (cutaway for clarity). On the inner catheter 2 in this embodiment, there aresensors 5 which measure the structuring 3′ of the guide wire 3 bycontacting and thereby make it possible to determine the mutual positionshift of inner catheter 2 and guide wire 3. If the sensor value,however, is a measure for the length between a fixed point and thelocation of the sensor (in the embodiment not shown here this would bethe Ohmic resistance), then it will be possible to determine a positionof only one single sensor value. FIG. 3 further shows a sensorevaluation unit 6, which records the sensor values of the sensors 5 andon the basis of these sensor values, and possible other fixedparameters, determines the position and/or position shift of the twobasic elements with respect to each other. The sensors 5 are contactedby means of supply wires 8. In the sensor evaluation unit 6 also voltagesources, if required, and similar supply sources should be integrated insuch a manner that no additional supply unit 4 is needed.

If the guide wire 3 is arranged such that it transmits light on thestructures 3′, the structures can be measured by means of an opticallysensitive sensor, such as a photo diode for example. For this purpose,the guide wire 3 itself can radiate in that it is made from a lucentmaterial or a material that can be excited to luminescence. The guidewire may also be a light conductor, however, where light is coupled outat the structures 3′. If the guide wire 3 comprises an opticallytransparent material, to which a phosphorescent material has been added,the guide wire can be excited to luminescence by prior exposure tolight. A structuring can be realized by optically opaque covers. If theinner catheter 2 provided with a photo diode is slid over the guide wire3, then the output signal of the photo diode would increase each time itbegins to travel over a lighting structure. The output signal will thendrop again as the photo diode is slid over an optically opaque cover.

Another embodiment of the guide wire 3 is obtained if the guide wireconsists of a material whose electrical conductivity is considerablyhigher than that of blood (this becomes necessary, because the catheteris at least partly filled with blood in intercoronary arterialapplications). The guide wire can be made of metal or some otherconductive material or mixture of materials, such as a conductiveplastic or a plastic metal mixture. To realize a structuring of such aguide wire, the guide wire is given an insulating coating, which isremoved or not deposited respectively at places for realizing thestructures 3′. The inner catheter 2 has at least a (ring-shaped)electrode, which is contacted by means of a flexible supply wire 8. Thesupply wire 8 is incorporated in the inner catheter 2, which can berealized, for example, during the manufacturing process of the innercatheter 2 by extrusion, or it is just glued onto it. The supply wire 8can be contacted at the other end of the inner catheter 2 (thereforetypically outside the patient). It is linked to the sensor evaluationunit 6 in the embodiment depicted here. The electrode is designed insuch a manner that it slides over the guide wire when the inner catheteris moved forward and backward and comes into contact with thenon-insulated tips. This can be realized, for example, by means ofresilient contacts or through brush contacts. The contacting need nottake place on the entire periphery. To ensure a good contact every time,however, three contact points are advisable on a circular ring electrodeenveloping the guide wire 3 (see FIG. 6). At these points, a smallerresistance is measured between guide wire and electrode than at theinsulated points, if the guide wire and electrode are linked to avoltage source. The internal resistance values of the voltage source andthe voltage must be selected appropriately so that only low currents aremeasured and there are no disturbing effects on the patient's body.

In a special embodiment of the invention, as shown by means of FIGS. 5and 6, the structurings 3′ with a width D3 are arranged on the guidewire 3. These structurings 3′ are points without insulation of theconductive material from which the guide wire is manufactured. FIG. 5shows a side view of the structured guide wire 3 with two ringelectrodes 5. The inner catheter 2, on which the ring electrodes 5 areprovided and the supply wires 8 of the electrodes are not shown here forthe sake of simplicity. FIG. 6 shows a cross section through the guidewire with a ring electrode and the contact points 5′ arranged on it. Inthis version, the two ring electrodes 5 have three contact points 5′each made of resiliently arranged warpings of electrode material,arranged on the periphery of the ring electrodes 5. The respectivedouble arrows show an elasticity of the contact points 5′ in the radialdirection, such that the contact points follow the changing radii of theguide wire at the insulated (radius R1) and the non-insulated points(shown by the dashed periphery of the guide wire 3 in FIG. 6; at thesepoints the guide wire 3 has the smaller radius R2), without losingcontact to the surface of the guide wire. The contact points 5′ aremutually offset by 120°, so that contact to the guide wire 3 is alwaysensured. Contact points 5′, which can adapt to a changing diameter, canalso be made as brush contacts. The two ring electrodes 5 are arrangedat a center-to-center distance D2 on the inner catheter 2, not shown,and contacted by means of supply wires. The length of the insulatedpoints on the guide wire 3 is D1. D1 and D3 are selected in the versiondescribed here, so that they are always larger than the center-to-centerdistance D2 between the ring electrodes. The result of this is thatthere is always a position on an insulated or on a non-insulatedstructure where both electrodes 5 either have contact with the guidewire 3 or no contact.

By means of the two ring electrodes 5 positioned at center distance D2,the position shift of inner catheter 2 with respect to guide wire 3 canbe determined. In the initial position drawn here, both ring electrodes5 have no contact to one of the structurings 3′ and therefore a highresistance is measured on both ring electrodes. If the inner catheter 2is moved on the guide wire 3 in the direction of the arrow V, then theelectrode arranged forward seen in shift direction V first comes intocontact with the non-insulated structuring and then the electrodearranged at the back seen in shift direction V comes into contact sothat a low resistance to the guide wire 3 is measured in the dashedshifting position of the ring electrodes for both electrodes. If themove continues in the direction of shift V, then the electrode arrangedin front loses contact first and then the electrode arranged at the backin the direction of shift loses contact. The sensor evaluation unit 6then simply counts the structurings 3′ traveled past and a valuecorresponding to it (e.g. the actual shift distance which can becomputed by means of the fixed given values of D3 and D1) can bedisplayed to the user of the catheter arrangement, for example, on adisplay on the sensor evaluation unit 6. The special arrangement of thering electrodes and structurings in this version makes it possible forthe sensor evaluation unit 6 to recognize whether the direction of shiftis changed during the shift. If, for example, the direction of shift ischanged when both electrodes have no contact, then the next contact ismeasured on the electrode being at the back in the former direction ofshift, which can be recognized by the sensor evaluation unit 6.Similarly, the electrode being at the back in the former direction ofshift loses contact first, if the direction of shift is changed, whileboth electrodes have contact. If the direction of shift is changed whileonly one electrode has contact, this also leads to a recognizabledeviation from the behavior as has been described for a constantdirection of shift. The precision of positioning achieved depends on theselected distances D1, D2 and D3. For intercoronary arterialapplications, a position determination of about one millimeter issufficient and D1 could be one millimeter, D3 half a millimeter and D2one third millimeter. According to the requirements and technicalboundary conditions, other values could also be selected. Thedetermination of the position or position shift can become more accurateby assessment of the sensor value (both electrodes have contact, onlyone electrode has contact, both electrodes have no contact) than by justcounting the structures passed. If D1 and D3 are known, then the shiftdistance during counting can be indicated in units of D1+D3. If thecontact signals are evaluated, then on loss of contact for bothelectrodes, an intermediate value of about (D1+D3)/2, can be added tothe shift path. The inaccuracy of this information depends on thedistance values selected.

If it is required that the inner catheter 2 is to be moved withoutchanging the direction of shift, then an embodiment with only oneelectrode 5 is of advantage, because then only the number of structuredpoints 3′ needs to be counted to achieve the determination of a positionshift. Such a version is simpler and more cost-effective to make fromthe point of view of manufacturing technology. If the direction of shiftchanges, this can be communicated to the sensor evaluation unit 6, forexample, manually, by pushing a button. Subsequently, the change in theshift distance is counted in the other direction on the basis of thecounted structurings 3′.

In another embodiment the ring electrodes 5 are embodied without thecontacting points 5′. Without a direct or conductive contact betweenring electrodes 5 and structurings 3′ the structurings passed can bemeasured capacitively. In this contactless embodiment, it isadvantageous if the voltage supply is not DC voltage but provided by ahigh-frequency source. Furthermore, embodiments with inductivemeasurement can be made, where the ring electrodes 5 are replaced bycoils, which have two supplies each. Accordingly, the structurings 3′are to be executed as coils on the guide wire 3.

1. A catheter arrangement, which comprises at least a first basicelement and a second basic element which is movably arranged over atleast a part of its length within the first basic element, and whichcatheter arrangement has a sensor unit provided for generating at leasta sensor value which is assigned to a measurable property of thecatheter arrangement, for determining a position and/or a position shiftof the first basic element and the second basic element to each other.2. Catheter arrangement, as claimed in claim 1, wherein the sensor unithas at least a first sensor, which is arranged on one of the basicelements and in that another one of the basic elements has the propertymeasurable by the first sensor.
 3. Catheter arrangement as claimed inclaim 2, wherein the measurable property is a structuring.
 4. Catheterarrangement as claimed in claim 2, wherein the first sensor is providedfor contactless measurement of the measurable property.
 5. Catheterarrangement as claimed in claim 3, wherein the structuring is a regularstructuring varying in the direction of the possible mutual shift of thefirst and second basic elements.
 6. Catheter arrangement as claimed inclaim 5, wherein at least a second sensor is arranged on the same basicelement Was the first sensor sand both sensors are provided to measurethe regular structuring.
 7. Catheter arrangement as claimed in claim 6,wherein the regular structuring is a structuring of an electromagneticproperty.
 8. Catheter arrangement as claimed in claim 2, wherein thesensor unit has a sensor evaluation unit, which is coupled to the firstsensor and which is provided for determining the position and/orposition shift from the sensor value.
 9. Catheter arrangement as claimedin claim 1, wherein the first basic element is embodied as elongated andhollow.
 10. Method for determining a position and/or position shift of afirst basic element and a second basic element of a catheter arrangementto each other, in which method the second basic element is arranged suchthat it can be moved over at least a portion of its length in the firstbasic element, in which a sensor unit generates at least a sensor valuethat is assigned to a measurable property of the catheter arrangement.